A polycarbonate resin is excellent in, for example, transparency, mechanical properties, thermal properties, electrical properties, and weatherability, and has been used in an optical molded article, such as a light-guiding plate, a lens, or an optical fiber, through the utilization of its characteristics. However, the light transmittance of the polycarbonate resin serving as one of the indicators representing its transparency is lower than that of, for example, a polymethyl methacrylate (PMMA). Therefore, a surface light source body including a light-guiding plate made of the polycarbonate and a light source has a problem in that its luminance is low.
Accordingly, a method of improving a luminance or a light transmittance in the light-guiding plate made of the polycarbonate has hitherto been proposed. In, for example, PTL 1, there is a disclosure of an aromatic polycarbonate resin composition and a light-guiding plate each including an aromatic polycarbonate resin and a thermoplastic resin whose refractive index differs from that of the aromatic polycarbonate resin by 0.001 or more, and each having specific optical characteristics. In PTL 2, there is a disclosure of an aromatic polycarbonate resin composition for a light-guiding plate having a satisfactory transmittance and a satisfactory hue, the composition being obtained by incorporating, into an aromatic polycarbonate resin, a specific amount of a polyalkylene glycol having a specific structure or a fatty acid ester thereof.
In PTL 3, there is a disclosure of a resin composition excellent in light transmittance and luminance, and capable of resisting molding at high temperature, the composition being obtained by blending an aromatic polycarbonate resin with a specific amount of a polyoxytetramethylene-polyoxyethylene glycol having a specific structure, and an optical molded article using the composition.
A polycarbonate resin composition to be used in the production of a light-guiding plate or the like has started to be molded in a wide temperature region in association with the thinning of a molded article thereof, and hence has been required to have: such high heat stability that its yellowing, a reduction in its light transmittance, or the like does not occur under a high-temperature condition; and durability at the time of the use of the product.
In PTL 4, there is a disclosure that the incorporation of a diphosphite compound having a specific structure and an alicyclic epoxy compound into an aromatic polycarbonate resin provides a molded article that is excellent in heat stability in high-temperature molding, light transmittance, and luminance, and that does not cause discoloration or cracking even when exposed to a high-temperature and high-humidity environment for a long time period.